THE  PARASITOLOGY  OF  THE  TOMATO 
FUSARIUM 


BY 


PAUL  JONES  BYRD 
A.  B.  WABASH  COLLEGE 

1917 


THESIS 


Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the 

Degree  of 


MASTER  OF  ARTS 
IN  BOTANY 


IN 


THE  GRADUATE  SCHOOL 

OF  THE 

UNIVERSITY  OF  ILLINOIS 


1921 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


_191_ 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY Paul  J.  Byrd 

F.NTTTT  ED  Tl  J P i t C I C "Y  of  th3  T ~ 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF '.tar  of  Art* 


Head  of  Department 


Recommendation  concurred  in* 


Committee 


on 


Final  Examination* 


*Required  for  doctor’s  degree  but  not  for  master’s 


/ \ jr.iC  'TO 


. 


. 


* 


TABLE  OF  CONTENTS 


Page 

I.  Introduction 1 

A.  The  tomato  wilt  disease 1 

1.  Names i 

2.  Nature  of  the  disease. 1 

3.  Diseases  confused  with  tomato  wilt....  2 

B.  Distribution  and  importance 3 

C.  History 3 

II.  Methods 7 

A.  Inoculations 7 

B.  Preparation  of  diseased  material  for  study.  8 

III.  Symptoms 10 

A.  External  symptoms 10 

B.  Internal  symptoms 11 

IV.  Correlation  of  symptoms  with  histology 12 

A.  Discoloration  of  parts. 12 

B.  Distribution  of  fungus  in  the  vascular 

bundles 13 

V.  Conclusion Id 

VI,  Bibliography. 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/parasitologyoftoOObyrd 


I.  Introduction 


The  disease  with  which  this  paper  deals  is  Known  as 
tomato  wilt,  Fusarium  wile,  sleepy  disease  and  blight.  The  name 
tomato  wilt,  since  it  is  more  descriptive,  is  more  generally  used. 
The  causal  organism  is  known  as  Fusar ium  lycopersici  Sacc.  It 
belongs  to  a group  of  fungi  of  very  similar  morphological  char- 
acters, such  as  those  organisms  that  produce  wilt  of  melons, 
cotton,  cowpea  and  cabbage. 

Fusarium  lycopersici  lives  as  a saprophyte  in  the  soil, 
where  it  attacks  the  young  roots  of  the  tomato  plant.  It  has 
not  been  definitely  determined  just  where  and  how  the  fungus 
penetrates  the  roots,  but  discolored  areas  on  the  young  roots 
ere  easily  seen  and  may  perhaps  be  points  at  which  the  fungus 
enters.  .After  entering  the  young  roots  it  finds  its  way  to  the 
large  vessels  of  the  f ibrovascular  bundles  and  follows  these  into 
the  stem  where  it  grows  rapidly  upward. 

The  fungus  produces  two  types  of  conidia,  the  small 
single-celled,  hyaline  microspores  and  the  large  falcate,  hyaline, 
septate  macrcspores.  In  the  latter  there  are  usually  three 
septa  though  there  is  often  only  one  and  sometimes  as  many  as 
five. 


There  are  several  other  diseases  of  the  tomato  which 


. 


-3- 


are  often  mistaken  for  the  tomato  wilt,  such  as  bacterial  blight, 
early  blight,  Sclerotium  wilt  and  mosaic.  Bacterial  blight  is 
quite  common  in  the  tomato -growing  areas  of  the  South  and  is 
often  found  in  the  same  field  with  the  fusarial  wilt  with  which 
it  is  quite  frequently  confused.  However,  with  bacterial  blight 
the  leaves  do  not  show  the  slow  yellowing  and  wilting,  but  rather 
wilt  quickly,  and  in  a short  time  the  whole  plant  is  dead.  In 
the  case  of  the  fusarial  wilt  it  is  the  f ibrovascular  bundles 
which  become  blackened,  the  pith  and  cortex  remaining  uninjured, 
while  the  bacterial  blight  organism  attacks  the  pith  and  cortex 
as  well  as  the  vascular  system. 

Early  blight  is  a leaf  disease  causing  definite  black 
spots  and  is  easy  to  distinguish.  It  becomes  severe  enough  at 
times  to  cause  defoliation.  The  interior  of  the  stem  is  not 
blackened. 

Sclerotium  wilt  is  a disease  of  the  stem  of  the  tomato 
plant  at  the  surface  of  the  ground.  The  cortex  of  the  stem  and 
the  cambium  layer  are  often  rotted.  The  plants  may  wilt  rapidly 
but  there  is  no  blackening  of  the  internal  tissues.  An  abun- 
dance of  mycelium  is  usually  produced  in  the  affected  area  of 
the  stem  ana  small  sclerotia  are  also  often  developed. 

Mosaic  is  a disease  of  the  leaves,  causing  a mottling 
or  dwarfing.  The  plants  are  seldom  killed,  but  appear  unhealthy. 
The  stem  is  unaffected. 

The  fusarial  wilt,  according  to  Edgerton  (b),  occurs 


-o- 


&11  over  the  world  though  it  is  more  abundant  in  the  warmer  re- 
gions. In  the  United  States  the  disease  has  been  reported  by 
workers  generally  in  the  southern  states  and  less  frequently  in 
the  northern  tier  of  states.  It  has  been  reported  in  the  Plant 
Disease  Survey  Bulletin  of  the  U.  S.  Department  of  Agriculture  as 
occurring  with  more  or  less  severity,  depending  on  the  weather 
conditions,  in  all  of  the  northern  states  east  of  the  Mississippi 
River.  For  instance,  it  ha 3 been  reported  as  general  in  Indiana 
for  1916  and  191?,  and  as  being  severe  in  1913.  In  Illinois  it 
has  been  reported  as  local  for  1911  and  1912  and  as  general  and 
severe  in  1917 . It  is  said  to  cause  much  damage  in  Pennsylvania 
every  year.  The  greatest  damage,  however,  occurs  in  the  Gulf 
States.  In  1919  Georgia  lost  40 $ of  its  entire  crop;  a loss  of 
30$  is  reported  from  Texas;  Mississippi  lost  15$;  Louisiana  and 
Alabama  each  lost  25$  of  their  entire  crops;  the  same  year  Ohio 
had  10$  of  its  crop  destroyed,  Illinois  4$  and  Indiana  3$.  The 
loss  for  a total  of  23  states  for  the  year  1919  was  4£$  of  the 
crop.  In  the  Southwest  the  tomato  crop  is  injured  to  some  extent 
by  the  wilt  disease.  Kansas  lost  8$  of  its  crop,  Missouri  5$, 
Oklahoma  3$  and  California  3$  in  1919.  The  importance  of  the 
tomato  wilt  is  clearly  shown  by  the  above  figures. 

The  literature  upon  tomato  wilt  is  rather  scattering. 
Although  the  disease  has  been  known  for  some  time,  prior  to  1916 
little  was  published  except  notes  on  its  occurrence. 


The  name  Fusarium  lycopersic i was  first  given  by  Sac- 


- • 


-4- 


oardo  (6)  in  1882  to  a fungus  which  he  studied  growing  on  tomato 
fruits.  The  fungus  which  causes  tomato  wilt  is  not  usually  found 
on  decaying  fruit,  although  Wollenweber  (10)  reports  having  suc- 
cessfully inoculated  the  fruit. 

Most  of  the  investigations  have  been  carried  on  within 
the  last  ten  or  twelve  years,  breeding  for  resistant  varieties 
being  especially  considered.  Norton  (7)  was  one  of  the  first 
to  work  with  resistant  varieties  while  Essary  (4),  Edgerton  and 
Moreland  (3),  Humbert  (5),  Burst  (2)  and  others  have  contributed 
to  this  phase  of  the  work,  Wollenweber  (10)  and  Sherbakoff  (9) 
have  determined  the  morphological  and  physiological  differences 
in  the  genus  Fusarium. 

Massee  (6)  in  1895  was  one  of  the  first  to  publish 
anything  of  a technical  nature  on  the  disease,  giving  a short 
account  of  the  life  history  of  the  fungus,  and  of  two  stages  of 
the  organism. 

The  question  of  the  effect  of  certain  chemicel  substances 
in  the  soil  on  the  development  of  the  tomato  wilt  fungus  has  beer- 
studied  at  the  Louisiana  experiment  station  (3).  The  results 
shew  that  corrosive  sublimate  when  added  in  large  quantities, 
about  335  pounds  to  the  acre,  will  eliminate  the  organism.  How- 
ever, this  substance  when  present  in  the  soil  in  such  quantities 
greatly  interferes  with  the  germination  of  the  tomato  seed.  Lime 
and  formaldehyde  treatment  of  the  soil  have  been  shown  to  give 
the  best  results  for  controlling  the  fungus.  It  was  found 


' 


- 


’ 


. 


experimentally  that  there  was  a decrease  in  the  amount  of  the  wilt 
with  an  increase  in  the  amount  of  lime  and  the  fungus  seemed  to 
be  delayed  in  its  development  though  it  was  not  entirely  eradi- 
cated from  the  soil,  even  with  the  heaviest  application  of  lime. 

Wilt  has  developed  on  plants  growing  in  soil  known  to 
be  free  of  the  wilt  organism  at  the  time  the  plants  were  set  out. 

/ case  of  this  kind  suggested  the  idea  that  the  seed  could  carry 
the  spores  of  Fusarium  lycoperaici , and  by  experiment  (3)  it  was 
proved  that  plants  may  become  infected  from  seed  which  carry  the 
wilt  spores.  Tomato  seeds  which  were  aseptic  were  trea.ted  with 
a spore  suspension,  dried  and  allowed  to  remain  in  a dry  place 
for  a year,  after  which  time  they  were  plant ed  in  sterile  soil. 

The  plants  coming  from  unese  seeds  showed  typical  wilt  symptoms 
while  the  checks  were  free  from  the  disease. 

There  is  not  much  known  about  the  activities  of  the 
wilt  organism  in  the  soil.  It  is  quite  possible  that  it  can 
live  for  at  least  two  years  in  a soil  where  there  are  no  tomatoes 
grown.  However,  because  a field  develops  wilt  after  it  has  been 
planted  in  some  other  crop  for  several  years  does  not  mean  that 
the  Fusarium  organism  has  remained  viable  in  the  soil  all  this 
time.  There  are  a greet  number  of  ways  that  a field  might  be- 
come infected.  The  organism  might  be  brought  in  from  other 
fields  in  surface  water,  or  the  spores  ma}'  be  blown  in  from 
neighboring,  infested  fields.  .Again  a great  many  fields  become 
infested  from  plants  which  have  been  grown  in  infested  beds. 


. 


• . 


-6- 


One  of  the  first  cases  of  the  disease  known  in  the  State  of 
Indiana  was  traced  to  infested  seed  beds  in  Florida. 

A knowledge  of  the  effect  of  varying  temperatures  on 
an  organism  is  very  essential  when  a study  of  its  parasitology 
is  being  made.  The  fusarial  wilt  organism  has  been  found  to 
have  an  optimum  temperature  of  about  28°,  a maximum  temperature 
of  3?c,  and  a minimum  below  14°  (3).  It  is  interesting  to  note 
that  the  highest  infection  percentage  results  when  the  soil  tern- 
perature  remains  close  to  the  optimum  for  the  growth  of  fungus. 

The  present  invest igat ions  have  been  carried  on  with 
the  hope  of  determining  the  correlation  between  the  external 
and  internal  symptoms  of  the  fusarial  wilt. 


i 


II . Methods 

Pure  cultures  of  Fusarium  lycoperslci  growing  on  prune 
juice  media  were  received  from  R.  E.  Smith  of  the  California 
Agricultural  Experiment  Station.  Pure  cultures  of  the  organism 
Y*ere  also  received  from  E.  E,  Clayton  of  the  Ohio  Agricultural 
Experiment  Station.  These  cultures  were  kept  alive  during  the 
experiments  by  transferring  every  few  weeks  to  fresh  potato  pep- 
tone media.  Pure  cultures  were  also  grown  on  washed  and  corn- 
meal  agar.  The  fungus,  however,  did  not  grow  well  on  these 
media  and  they  were  finally  discarded. 

A.  large  number  of  stems  of  tomato  plants  which  had  been 
killed  by  the  Fusarium  organism  were  received  from  the  Tennessee 
Agricultural  Experiment  Station.  These  stems,  which  were  per- 
fectly dry,  were  ground  in  a food  chopper.  The  resulting  powder 
and  fragments  were  thoroughly  mixed  with  the  upper  soil  of  the 
seed  beds  in  the  green- house.  Tomato  seed  of  the  Ponderosa 
variety  were  then  sown  in  this  soil.  Plants  were  also  started 
in  small  flats  and  when  they  grew  to  be  four  or  five  inches  tall 
they  were  transplanted  into  the  inoculated  soil  in  the  seed  bed. 
These  plants  showed  the  first  symptoms  of  the  disease  at  the 
same  time  as  did  those  that  were  started  in  the  diseased  soil. 

In  order  to  learn  whether  the  Fusarium  would  grow  on 
the  surface  of  tomato  plants,  a number  of  as#eptic  seeds  were 


. 


. 

' 

. 


* * 

. 

. . '■  ; . -i 

-8- 


sown  in  a sterile  moist  chamber  on  filter  paper  and  allowed  to 
germinate.  The  seedlings  were  inoculated  by  atomizing  with  a 
heavy  spore  suspension  of  the  wilt  fungus.  These  moist  chambers 
were  kept  in  a warm  place  and  the  seedlings  studied  from  time  to 
time  as  the  fungus  developed. 

To  ascertain  the  distribution  of  the  wilt  organism 
within  the  host  a plant  about  60  c.m.  tall,  which  showed  typical 
wilt  symptoms,  w as  removed  from  the  green-house  and  taken  to  the 
laboratory.  Here  an  outline  diagram  was  made  of  the  stem  and 
branches,  divided  into  numbered  regions.  Samples  from  each 
region  were  then  sectioned  with  the  hand  microtome;  dehydrated 
and  decolorized  in  alcohol,  cleared  in  xylol  and  mounted  perman- 
ently in  balsam.  By  arranging  these  mounts  in  sequence  accord- 
ing to  the  diagram  it  is  possible  to  study  the  distribution  of 
the  fungus  within  the  host . 

Free  hand  sections  of  the  diseased  regions  were  also 
made  and  treated  with  the  differential  stain,  Pianese  III.B. 

The  mounts  of  this  material  show  the  mycelium  of  the  organism  in 
the  large  vessels  of  the  fibro vascular  bundles.  (Plate  I.) 

A diseased  tomato  plant  was  taken  from  the  green- house 
and  placed  in  95 $ alcohol  and  allowed  to  remain  for  three  weeks, 
after  which  time  it  was  placed  in  100$  alcohol  for  two  weeks. 

This  process  dehydrated  and  decolorized  the  tissue  thoroughly. 

The  specimen  was  then  cleared  by  placing  it  in  xylol.  /fter  a 
few  days  the  discolored  vascular  bundles  could  be  traced  from 


. 

. . 

y* 

• 

. 


The  darkened  bundles  were 


_c  _ 


the  bottom  of  the  stem  to  the  rop. 
clearly  visible  in  the  petioles  of  the  leaves.  Plate  II.  shows 
a portion  of  the  plant  after  it  was  subjected  to  the  above  treat 
ment . 


-10- 


III.  Symptoms 

The  wilt  disease  may  occur  on  tomato  plants  in  any 
stage  of  their  development.  In  the  green-house  it  becomes 
most  noticeable  about  blossoming  time.  The  disease  first  shows 
externally  in  the  lower  leaves.  The  tips  of  these  leaves  first 
turn  yellow  and  this  yellowing  gradually  spreads  over  all  the 
leaf.  The  leaves  then  soon  wilt  and  die.  fls  the  disease 
progresses  upward  through  the  main  stem  more  of  the  leaves  turn 
yellow  and  dry  up  and  finally  the  7/hole  plant  may  die.  The  time 
intervening  between  the  first  appearance  of  the  disease  and  the 
death  of  the  plant  varies,  due  perhaps  to  resistance  in  the  plant 
or  to  other  factors  not  known. 

Under  green-house  conditions  but  few  fruits  set  on 
diseased  plants.  In  cases  where  fruits  do  set  they  remain 
small  and  ripen  prematurely.  Some  plants  become  30  badly  in- 
fected that  they  do  net  grow  to  be  very  large,  succumbing  rapid- 
ly. On  the  other  hand  some  plants  do  not  show  external  signs 
of  infection  until  they  are  from  four  to  six  weeks  old  and  suc- 
cumb slowly. 

The  root 8,  as  well  as  the  other  parts  of  the  plant, 
show  external  signs  of  the  disease.  They  appear  yellow  and  in 
the  case  of  the  smaller  ones  often  turn  black  and  rot.  If  a 
diseased  plant  is  palled  up  the  ends  of  the  primary  roots  and 


« 


-11- 


many  of  the  secondary  roots  break. 

The  internal  appearance  of  an  infected  plant  is  very 
characteristic.  The  best  method  of  diagnosis  of  this  disease 
is  to  cut  the  stem  of  the  diseased  plant  and  observe  the  dis- 
coloration of  the  tissue.  In  the  stem  the  fungus  confines  it- 
self to  the  f ibrovascular  bundles  which  are  turned  a brownish 
color.  In  the  case  of  the  roots  all  of  the  tissues  are  dis- 
colored. The  leaves  which  have  turned  yellow  show  discolored 
veins.  This  discoloration  is  continuous  from  the  vascular 
bundles  of  the  stem  out  into  the  petiole  and  blade  of  the  leaf. 
In  a young  plant  which  is  infected  the  darkened  vascular  system 
may  be  seen  clearly  by  holding  the  plant  up  to  the  light. 


-12- 


IV.  Correlation  of  Symptoms  with  Histology 

The  roots  of  seedlings  grown  in  a moist  chamber  on 
filter  paper  and  inoculated  with  the  wilt  organism  shewed  a 
general  browning  five  days  after  inoculation.  By  microscopic 
study  the  internal  tissues  of  these  roots  were  also  found  to 
show  this  general  browning.  The  mycelium  of  the  causal  organ- 
ism was  found  in  abundance  in  the  cells  of  the  cortical  tissue 
(Plate  III.).  This  general  browning  of  the  internal  tissues 
and  cortex  was  also  found  to  be  characteristic  of  the  roots  of 
diseased  plants  grown  in  soil  in  the  green-house.  - .As  soon  as 
the  fungus  reaches  the  region  of  the  stem  just  above  the  ground 
it  confines  itself  to  the  f ibrovascular  bundles.  The  leaves 
of  a diseased  plant  do  not  wilt  in  the  order  of  their  height,  as 
the  fungus  progresses  up  the  stem.  The  lowest  leaves  may  first 
show  signs  of  wilting  while  the  next  to  wilt  may  be  a leaf  near 
the  top  of  the  stem  (Plate  IV.). 

About  two  or  three  weeks  after  the  plant  becomes  in- 
fected, or  after  the  lower  leaves  are  all  dead,  the  stem  near 
the  ground  loses  its  green  color  and  has  a brownish  tinge.  This 
color,  which  gradually  becomes  darker  a3  the  plant  becomes  older, 
advances  up  the  stem  as  the  fungus  inside  advances.  The  whole 
plant,  however,  does  not  show  this  general  discoloration  until 
some  time  after  the  last  leaf  has  wilted  and  died.  (Plate  V.) 


* - 


-13- 


Fibrovascular  bundles  in  which  the  mycelial  6trands  of 
Fusarium  lycopersici  grow  are  turned  a dark  brown  color.  This 
characteristic  discoloration  is  not  only  seen  in  the  vessels  in 
which  the  mycelium  is  growing  but  can  be  seen  in  the  bundles  just 
ahead  of  the  advancing  fungus.  This  discoloration  is  perhaps 
due  to  some  toxic  substance  or  enzyme  secreted  by  the  fungus. 

The  wilting  and  final  death  of  the  plant  may  be  due  to  such  sub- 
stance, and  not  to  the  cutting  off  of  the  water  supply  by  the 
plugging  of  the  vessels  by  the  mycelium  of  the  fungus,  as  is 
generally  thought  to  be  the  case.  Of  the  numerous  sections  of 
diseased  stems  that  have  been  studied  only  a very  few  have  shown 
the  water-conducting  vessels  to  be  entirely  plugged  by  the  fungus. 

The  mycelium  in  the  vascular  system  does  not  make  the 
same  upward  progress  in  each  of  the  bundles.  Plate  VI.  shows 

outlines  of  sections  of  a diseased  tomato  stem  taken  from  the 
regions  indicated  on  the  diagram  of  the  whole  plant  in  Plate  VII. 
The  relative  degree  of  blackening  in  each  bundle  is  shown  by  the 
shading.  In  the  primary  root,  section  P,  all  of  the  fibrovas- 
cular  bundles  showed  a general  discoloration,  which  is  rather  to 
be  expected  since  the  entire  cortex  of  the  root  was  discolored. 

Bundle  No.  1,  Plate  VI  .,  was  found  to  be  discolored 
almost  the  entire  length  of  the  stem.  Bundles  No.  2 and  3 show 
the  characteristic  blackening  to  within  about  7 cm.  of  the  top 
of  the  stem.  The  discoloration  in  bundle  No.  4 extended  to 
within  about  9 cm.  of  the  'top  of  the  stem,  while  bundle  No.  5 was 


-14- 


dark  ened  only  to  about  9 cm.  above  the  ground. 

The  petioles  of  the  leaves  which  showed  typical  wilting 
caused  by  the  fungus,  as  well  as  those  which  remained  normal,  were 
sectioned,  and  a study  of  their  vascular  tissue  made.  Sections 
No.  1,  3,  5 and  8 are  of  petioles  the  leaves  of  which  shewed  ex- 
ternal signs  of  wilting,  and,  as  shown,  Plate  VI.,  all  of  the 
vascular  bundles  were  blackened.  Sections  No.  8 and  9 are  of 
petioles  the  leaves  of  which  externally  appeared  normal.  In 
this  case  the  bundles  were  not  the  least  discolored.  We  &s,y 
say  that  there  is  no  wilting  unless  the  vascular  bundles  have 
the  typical  discoloration.  It  might  be  added  that  a number  of 
stems  and  petioles,  the  leaves  of  which  externally  did  not  appear 
to  be  infected,  as  well  as  number  which  showed  typical  infec- 
tion symptoms  have  been  sectioned  during  the  course  of  these 
observations  and  that  the  above  statement  applies  in  every  case. 


-15- 


] 


V.  Conclusion 

The  attack  of  the  fusarial  organism  upon  the  tomato 
plant  is  confined  to  certain  tissues,  namely  the  cortex  and 
f ibrovascuier  bundles  of  the  roots  and  the  f iforovascular  bundles 
of  the  stem.  The  mycelium  in  the  cortex  of  the  root  gees  from 
cell  to  cell  passing  through  the  walls. 

A plant  which  shows  external  3igns  of  wilting  is  always 
found  to  have  discolored  vascular  bundles.  /II  the  bundles  may 
have  this  discoloration  at  the  surface  of  the  ground,  while  a 
few  centimeters  up  the  stem  only  one  or  two  show  the  darkening. 

In  some  diseased  plants  a discolored  bundle  may  run  the  full 
length  of  the  plant . 

The  blackening  of  the  bundles  is  not  confined  to  the 
portion  of  the  bundle  in  which  the  mycelium  is  growing,  but  is 
evident  in  vessels  perceptibly  in  advance  of  the  mycelium. 

The  stem  of  an  infected  plant  assumes  a brownish  color- 
a few  weeks  after  the  wilting  of  the  leaves.  This  external 
browning  of  the  stem  is  always  associated  with  the  typical  in- 
ternal infection. 

The  tissues  of  the  roots  of  a diseased  plant  show  dis- 
coloration internally  as  well  as  externally.  The  ends  of  in- 
fected root 6 quite  often  show  marked  rotting. 


' 


VI.  Bibliography 


(1)  Clayton,  E.  C.  The  Relation  of  Soil  Temperature  to  the 

Development  of  the  Tomato  Fusarium  Wilt.  (Abs.)  Phyto- 
path. 10:  63-64.  1820. 

(2)  Durst,  C.  E.  Tomato  Selection  for  Fusarium  Resistance. 

(Pta.)  Phytopath.  8:  85.  1918. 

(3)  Edgerton,  C.  W.,  and  Moreland,  C.  C.  Tomato  Wilt.  Louisi- 

ana Agr.  Exp.  St a.  Bull.  174.  1820. 

(4)  Essary,  S.  H.  Notes  on  Tomato  Diseases  with  Results  of 

Selection  for  Resistance.  Tennessee  Agr.  Exp.  Sta.  Bull. 
95.  1812. 

(5)  Humbert,  -J.  0.  Tomato  Diseases  in  Ohio.  Ohio  P gr . Exp. 

Sta.  Bull.  321.  1918. 

(6)  Masses,  0.  P Disease  of  Tomatoes.  Gardener's  Chronicle. 

Ser.  3,  17:  707-708.  1895. 

(7)  Norton,  J.  B.  S.  Tomato  Diseases.  Maryland  £g r.  Exp.  Sts. 

Bull.  180:  102-114.  1914. 

(8)  Saccsrdo,  P.  P . Sylloge  Fungorum  Omnium  Hucusque  Cognitorum. 

4:  705.  Padua. 1886. 

(9)  Sherb&koff,  0.  D.  Fusaria  of  Potatoes.  Cornell  Univ.  P gr. 

Exp.  Sta.  Memoirs.  6.  1915. 

(10)  Wollenweber,  H.  W.  Parasitic  Wilt  Diseases  of  Cultivated 
Plants  Due  to  Fungi.  Ber.  Deutsch.  Bot.  Gesells.  31: 
17-34.  18±3 . 


- 


. 


. 


Explanation  of  Plates. 


Plate  I ■ 

Fig.  A.  Photomicrograph  of  a section,  at  region  G,  of 
the  stem  represented  in  Plate  VII.,  showing  the  mycelial  3trands 
of  Fusarium  lycopersici  in  the  large  vessels  of  the  fibrovas- 
cular  bundles. 

Fig.  B.  Photomicrograph  of  a section,  at  region  B,  of 
the  same  stem,  showing  the  mycelial  strands  scattered  in  the 
large  ducts  of  the  bundles. 

Plate  II. 

A section  of  a diseased  tomato  stem  decolorized  and 
dehydrated  showing  the  discolored  vascular  bundles. 

Plate  III. 

Drawing  showing  the  mycelium  of  the  wilt  organism  in 
the  cortical  cells  of  the  root. 

Plate  IV. 

A diseased  tomato  plant  showing  the  wilted  leaves  on 
one  side  of  the  stem. 

Plate  V. 

A tomato  plant  killed  by  the  wilt  organism. 

Plate  VI. 

croso  sections  oi  tne  tomato  stem  made  at 
regions  shown  in  Plate  VII.,  showing  the  relative  amount  of 
blackening  in  each  bundle. 


PL4TE  II 


PL/TE  III. 


PLATE  IV. 


